E30 metric to standard gauge cluster question

I recently purchased an E30 318iS from Canada. As part of the federalization, I needed to replace the gauge cluster (metric) with a standard (miles) gauge cluster. So far, everything is peachy, except I've noticed that the fuel gauge only gets to 1/2 before the low fuel light comes on. Naturally, this is a problem. All other functions (tach, speedo, econogauge, water temp gauge) appear to function normally.

My question - is it sufficient to simply swap the code plug from the old metric gauge to the new standard gauge or do I need a new fuel sender as well? I couldn't find any "metric only" fuel senders listed on RealOEM so I'm a bit baffled.